In a digital communication system in the past, frequency selectivity and time fluctuation of a transmission line are caused by multipath fading that occurs when a transmission signal reflects on a building or the like and Doppler fluctuation that occurs because of movement of a terminal. In such a multipath environment, a received signal is a signal in which a transmission symbol and a delayed symbol, which arrives after a delay time elapses, interfere with each other.
As a method of obtaining a best reception characteristic in a transmission line having frequency selectivity, a single carrier transmission system attracts attention in recent years. For an increase in a volume of transmission data, there is an increasing necessity for multichannel transmission in which a single carrier is used. The multichannel transmission is a technology for simultaneously transmitting several channels or several different data sequences. For example, when the number of channels is represented as M, data for M users or M kinds (sound, image, moving image, etc.) of data are simultaneously transmitted. When the method of the multichannel transmission is used in this way, it is possible to simultaneously transmit data to a large number of users or simultaneously provide various services.
In the multichannel transmission in which a plurality of signals are multiplexed, there is a problem in that a PAPR (Peak to Average Power Ratio) value is high. In general transmission, for example, Patent Literature 1 described below discloses a technology for suppressing peak power in a communication system for a single carrier. Patent Literature 2 described below discloses a technology for changing a phase for each signal and suppressing peak power in another communication system different from the multichannel transmission. Patent Literature 3 described below discloses a technology for selecting a precoder that suppresses transmission peak power in a MIMO (Multiple Input Multiple Output) communication system.